The two haploid cell types (a and Alpha) of the yeast Saccharomyces cerevisiae each secrete specific peptide hormone-like molecules which trigger events leading to fusion ("mating") of the cells, a relatively simple developmental sequence. Because incisive genetic and biochemical studies can be performed in yeast cells, particular those utilizing recombinant DNA, it may be possible to learn the precise molecular details of peptide hormone biosynthesis and mode of action by examining the yeast mating pheromones (a-factor and Alpha-factor). The approaches to be taken include: (1) in vitro alterations of the control regions of the cloned Alpha-factor and a-factor genes, and novel gene fusions to indicator enzymes, to dissect the cell type-specific regulation of transcription of these genes; (2) specific antibodies, inhibitors, and mutations, in conjunction with the cloned genes, to provide probes and substrates for analyzing the synthesis, membrane translocation, post-translational processing, and secretory transport of the pheromone precursor proteins (prepro-Alpha-factor and prepro-a-factor); (3) [125I]-labelled pheromones, covalent cross-linking of reactive pheromone derivatives, affinity chromatography using matrix-bound pheromones, putative genes for Alpha-factor receptor (STE2) and adenylate cyclase (CDC35), and the cloned STE5 gene, to identify pheromone receptors and to examine the mechanism of pheromonal modulation of cyclic AMP synthesis; and, (4) transcript mapping, gene disruption, and DNA sequencing, to characterize the structure and function of cloned genes whose expression is under pheromonal control. In multicellular organisms, peptide hormones are responsible for cell-cell communications that are required during embryonic development and in the coordination of life functions in adults. The under- or over-production of particular peptide hormones, or the inability to sense their presence, have been correlated with numerous human diseases (e.g. dwarfism, Cushing's disease, and diabetes). Understanding of the fundamental aspects of the synthesis and release of peptide hormones, and the regulation of these processes, as well as the biochemical bases of their mechanisms of action, is necessary for effective diagnosis and therapy of such diseases. In addition, knowledge of the biosynthesis of yeast pheromones may allow the production of medically-valuable human hormones by yeast cells on a commercial scale.